U.S. Pat. No. 3,337,981 discloses a fishing float in which the boyancy is varied by rotating a pair of telescoping threaded members relative to each other to vary the volumn of an interior air chamber.
U.S. Pat. No. 4,944,113 discloses a fishing float in which the boyancy is varied by moving longitudinally a pair of telescoping members relative to each other to vary the volumn of an interior air chamber.